Question: How many nonnegative solutions are there to the equation $x^2 = -4x$?
Explanation: We can rearrange the equation as $x^2 + 4x = 0$.  Factoring gives $x(x+4)=0$, which has solutions $x=0$ and $x=-4$.  Only $\boxed{1}$ of these solutions is nonnegative.